A known yarn tension detecting apparatus is shown in FIG. 3. This yarn tension detecting apparatus comprises a ceramic yarn guide 7, an aluminum yarn guide support 4 to which the yarn guide 7 is directly fixed, an elastic substrate 3 to which the yarn guide support 4 is attached approximately perpendicularly and that is cantilever-supported by a housing 1, a strain measuring member 8 for measuring the strain in the elastic substrate 3 and a resistor 9 that corrects the effect of the temperature of the elastic substrate 3.
This yarn tension detecting apparatus uses the correcting resistor 9 to correct the effect of the temperature of the elastic substrate 3. Since, however, the yarn guide support 4 is composed of aluminum and a fixing screw 6 for the yarn guide 7 is composed of steel, a large amount of heat generated by the friction between the measured yarn Y and the yarn guide 7 is transmitted to the elastic substrate 3 via the yarn guide support 4. Thus, the elastic substrate 3, particularly its yarn guide support mounting position (axis position), becomes hot as shown by the continuous line in FIG. 2. As shown in this graph, the temperature of the position at which the strain measuring member 8 is located does not become so high because heat escapes from the supporting section to the housing 1, whereas the temperature of the position at which the correcting resistor 9 is located becomes very high. Thus, the correcting resistor 9 does not fulfill its inherent correcting function, which means that the yarn tension detecting apparatus is prevented from measuring the yarn tension accurately. This is pronounced when the measured yarn Y is travelling at a high speed.
It is an object of the present invention to prevent an elastic substrate of a yarn tension detecting apparatus from having a biased temperature distribution in order to enable accurate yarn tension measurements.